As an automotive repair expert at autelfrance.com, I often encounter questions about OBDII systems and readiness indicators. Recently, while performing routine maintenance on my own 1997 Porsche 993, I decided to conduct an informal test regarding OBDII readiness indicators, specifically focusing on how to ensure they are properly set for emissions testing. This experience highlighted the importance of understanding these indicators, particularly the Oxygen Sensor Heater (OH) indicator, for vehicle owners and technicians alike.
After disconnecting my 993’s battery for maintenance, I knew that this would reset the OBDII system’s readiness flags. These flags, or monitors, are crucial as they indicate whether a vehicle’s emission control systems have been tested and are functioning correctly. In many regions, including Tennessee where I reside, passing an annual emissions test is mandatory for vehicle registration renewal. This test often involves checking the OBDII system for readiness, not just a traditional “sniffer” test.
In the past, I’ve successfully used the “BMW OBDII Drive Cycle Procedure” to set readiness indicators on various vehicles. Confident in this method, I drove my 993 normally for what turned out to be over 1500 miles before checking the status of the monitors using my INNOVA 3100 code reader. This reliable tool, which I’ve owned for years, has proven invaluable for diagnosing OBDII related issues (excluding that one time I forgot to disable the immobilizer!).
Alt text: INNOVA 3100 code reader plugged into the OBDII port of a Porsche 993, preparing to check OBDII readiness indicators.
To my initial check, after extensive normal driving, revealed that only three monitors were set and ready:
- M – Misfire
- F – Fuel System
- CC – Comprehensive Component
However, five crucial monitors were still in a non-set, or flashing, condition:
- C – Catalyst
- EV – Evaporative System
- 2A – Sec. Air System (SAI)
- O – Oxygen Sensor
- OH – Oxygen Sensor Heater
It’s important to note that OBDII systems can support up to 11 monitors, but as my reader’s manual states, not all vehicles utilize all of them. In the case of my Porsche 993, it appears to support 8 monitors in total. The Oxygen Sensor Heater (OH) monitor, along with the others not yet set, are vital for ensuring the vehicle meets emission standards. The OH monitor specifically checks the functionality of the oxygen sensor heaters, which are essential for bringing the oxygen sensors to operating temperature quickly for accurate readings and efficient catalytic converter operation.
To expedite the process of setting the remaining monitors, I decided to employ the “BMW OBDII Drive Cycle Procedure”. On a Saturday morning, I performed the procedure for the first time, keeping the INNOVA 3100 reader connected throughout the drive to monitor the readiness status in real-time. The reader refreshes data approximately every minute, providing continuous feedback. Despite completing the drive cycle, none of the readiness indicators changed their status – the same three were set, and the five, including the OH indicator, remained flashing.
Alt text: OBDII code reader screen showing three readiness monitors set and five monitors, including Oxygen Sensor Heater (OH), not set prior to successful drive cycle completion.
After allowing the 993 to cool down for about four hours, I attempted a second run of the BMW drive cycle. This time, I chose a slightly different route but ensured it still allowed me to execute each step of the procedure in order. Again, the OBDII reader remained connected, and the monitor status remained unchanged throughout the drive. However, upon returning home and performing the final step – idling for approximately 5 minutes (as indicated for automatic transmissions, though applicable here as a general final step) – something remarkable happened. Within less than a minute of idling, all five remaining readiness indicators, including the Oxygen Sensor Heater (OH) monitor, switched to a set status! Success!
Alt text: OBDII code reader display showing all OBDII readiness indicators, including Oxygen Sensor Heater (OH), now set and ready after successful BMW drive cycle.
It’s important to clarify that strictly adhering to every speed and RPM limit of the “BMW OBDII Drive Cycle Procedure” can be challenging in real-world driving conditions. Frequent stops and turns often necessitate deviations. While I aimed to maintain the specified speeds and RPMs as much as possible, there were instances where I briefly exceeded the 3000 RPM or 60 MPH limit. However, these were minor and short-lived. The key is to attempt to follow the procedure as closely as possible without being overly rigid.
This experience underscores the effectiveness of drive cycle procedures in setting OBDII readiness indicators, including the often crucial Oxygen Sensor Heater (OH) monitor. For technicians and vehicle owners facing similar situations before emissions testing, understanding and correctly applying a drive cycle can be the key to a successful outcome. Remember to always consult your vehicle’s repair manual for the most accurate drive cycle procedure, although in some cases, like mine, a generic procedure can be surprisingly effective.
